1. Technical Field of the Invention
The present invention relates to rake device scraper arms for cleaning screens and perforated screens located in water conduits such as waste water treatment streams, power plants, sewers, and cooling water streams. More particularly, this invention relates to an improved scraper arm to hold a scraper to remove debris from the rake screen or perforated screen without wearing out the rake bar or screen elements.
2. Background of the Prior Art
Bar screens are used for screening solids and debris from flowing liquid streams. An example of such a bar screen system can be found in U.S. Pat. No. 5,730,862 issued to Mahr. In such systems, a series of rakes pass over parallel screen bars, which make up a bar screenfield and remove the debris collected from the flowing stream. Occasionally, large pieces of debris can plug the teeth on the rakes, causing the performance of the rakes to deteriorate. If the rakes do not perform properly, the bars within the bar screenfield can become plugged and eventually cause the water to overflow over the filter system. When this excessive pluggage occurs, the screen system must be cleaned by typically taking the screen system out of service for a relatively long period of time in order to clean the rakes.
Others have attempted to solve the problem of pluggage in the rakes by using such devices as brushes and scrapers to remove debris from the rakes. Brushes get clogged and do not operate very well after a short time period. Others have used scrapers to remove the debris from the rakes. Great Britain Pat. No. GB 1,525,871 issued to Crosby illustrates one example of a scraper. Weaknesses exist in prior scrapers due to the metal-to-metal contact between the scraper and the rake teeth. This metal-to-metal contact causes the scraper to wear out quickly, requiring replacement of the scraper assembly relatively fast.
A need exists for a way of cleaning the rakes within a bar screen system that can be performed quickly, safely, and cost effectively. A need also exists for the cleaning method to be reliable and be able to be used for an extended period of time. Ideally, such a system should be capable of being adapted to the specific fluid applications and also be able to be used on existing screen system equipment with minimal modification.
The present invention advantageously provides a screen system for removing debris from a flow channel. The screen system includes a screen frame having a bar screenfield that is located below a debris plate. The bar screenfield includes a plurality of bars. Rakes with a plurality of tines, or teeth, fit between the bars of the bar screenfield. The rakes are movable along the bar screenfield to clear the bar screenfield of debris. The screen system also includes a scraper mounted at the top of the screen system.
The scraper removes debris off of the rakes when the rakes reach the top of the screen system. Each rake raises the scraper as the rake reaches the top of the screen system while the scraper removes, or scrapes, the debris off of the rake. Once the scraper clears the rake, the scraper returns to an original position. The scraper contains a plurality of scraper arms that hold a scraper support plate attached to a scraper blade. At least some of the scraper arms have a set of wear guides. A curvature in front edges of the wear guides prevents metal tines, or teeth, in the rake from being worn down since the physical contact between the metal tines and the metal base arm is nonexistent.
So that the manner in which the features, advantages and objects of the invention, as well as others which will become apparent, may be understood in more, detail, more particular description of the invention briefly summarized above may be had by reference to the embodiment thereof that is illustrated in the appended drawings, which form a part of this specification. It is to be noted, however, that the drawings illustrate only a preferred embodiment of the invention and are therefore not to be considered limiting of the invention's scope as they may admit to other equally effective embodiments.
A screen system 31 is shown in
Screen frame 29 has a front edge 41 and a rear edge 43. When screen system 31 is installed in a channel 33, screen frame front edge 41 will be on the upstream side, and screen frame rear edge 43 will be on the downstream side. The distance between screen frame front edge 41 and screen frame rear edge 43 defines the depth dimension of screen frame 29. Bar screen 37 and debris plate 35 are attached to screen frame rear edge 43, with bar screen 37 located immediately below debris plate 35.
Bar screen 37 comprises a set of parallel, evenly spaced, vertical bars 17. The preferred embodiment of the screen system uses flat bars 17, which are trapezoidal in cross-section. However, the bars 17 can be constructed in various shapes. The leading edge of each bar in the preferred embodiment is wider than the trailing edge, to prevent debris from obstructing the screen. The bars 17 are spaced to allow liquid to pass unimpeded, but to block the passage of any debris or solids in the flow stream. Screen 37 contains enough bars 17 to extend across the entire width of screen frame 29. These solids and debris accumulate on the front of bar screen 37.
For illustrative purposes, in the preferred embodiment of the rake system, each rake 39 has a series of castellations or tines 45 to fit in the gaps between each bar 17. The shape of the tines 45 can vary depending upon the size of the gaps between each bar 17. Rakes 39 are attached at each end to endless chains 47. The two chains 47 carry rakes 39 in an upward direction over the front surface of bar screen 37. As each rake 39 travels upward along bar screen 37, tines 45 clean the accumulated solids and debris from bar screen 37. Solids and debris are carried to the top of screen system 31 for disposal.
As shown in
A scraper 10 is mounted at the top of a rake screen system 31, as illustrated in
The improved scraper 10 is shown in a three bar variation with a scraper blade 25 attached to the scraper arms 11. The scraper 10 is pivotally attached to the frame 29 of the screen system by a shaft 15 with a stop plate 13 at each end of the shaft 15, which limits the rotation of the scraper blade 25. The stop plates 13 rotate with shaft 15 and scraper arms 11 and contact a flange on the forward side 41 of frame 29 to stop the downward movement as shown in
FIG. 7. The scraper arm assembly 10 fits between the two sprockets 49. Scraper 10 can have more scraper arms 11 depending upon the length of the entire screen. The location of the scraper arms 11 can be varied along the shaft.
Wear guides 21 are thin plates. The front and back edges of the wear guides 21 are curved with the curved front edges 22 being slightly forward of the base arm 19. The wear guides 21 are bolted to the base arm 19, with one wear guide 21 on each side of the base arm 19 with the base arm 19 between the wear guides 21, as shown in FIG. 3. The wear guides 21 are shorter than the base arms 19 and are attached so that their front edges slightly protrude past the front edge of the base arm 19. The bottom edges of the wear guides 21 are slightly recessed above the bottom edge of the base arm 19.
Support plate 23 is a flat plate extending the width of the scraper 10. The support plate 23 is connected to the base arms 39, typically by welding, just below where the wear guides 21 sit.
Wing bars 40 are attached in pairs to the top edge of the tines 45 and the rake 39 at about a 45° angle and are parallel to each other. Wing bars 40 are constructed of metal bars. Wing bars 40 are only installed behind the two contact tines 45 for each scraper arm 11. The width of wing bars 40 is no thicker than the width of tines 45. Wing bars 40 prevent rake bar 17 from catching on scraper 10 in the event the rotational direction reverses.
In operation of the first embodiment, scraper 11 will retain the position of
As illustrated in
As scraper 10′ raises, spring ends 62, 63 move toward each other, decreasing the compression. As scraper 10′ begins to move back to the lower position, spring ends 62, 63 move apart, increasing the compression. Spring 67 tends to cushion the return of scraper 10′ to the lower position. Because scraper 10′ has to compress spring 67 when returning to the rest position, the rate of returning movement is slowed and the impact of pivot stop 13′ is cushioned. In screen systems with a width of over four feet, more than one spring 67 can be used.
In a third embodiment, which is shown in
The present invention has many advantages when compared to prior art systems. The first advantage is that the tines on the rake bars do not wear out as quickly since there is minimal contact with any of the tines. Since the tines do not wear out, the need to replace the rakes is significantly reduced. The spring and shock absorber embodiments further decrease wear on the scraper plate by cushioning the return of the scraper plate to its lower position.
While the invention has been shown or described in only some of its forms, it should be apparent to those skilled in the art that it is not so limited, but is susceptible to various changes without departing from the scope of the invention.
This application claims the benefit of a provisional application having U.S. Ser. No. 60/328,984, filed on Oct. 12, 2001, which hereby is incorporated by reference in its entirety.
Number | Name | Date | Kind |
---|---|---|---|
1912020 | Steindorf | May 1933 | A |
2128347 | Briggs | Aug 1938 | A |
2291103 | Plummer | Jul 1942 | A |
2978105 | Poheim | Apr 1961 | A |
3144406 | Crise | Aug 1964 | A |
4709804 | Duperon | Dec 1987 | A |
5565093 | Frankenberger | Oct 1996 | A |
5730862 | Mahr | Mar 1998 | A |
6309540 | Chang | Oct 2001 | B1 |
Number | Date | Country |
---|---|---|
1373342 | Nov 1974 | GB |
1525871 | Sep 1978 | GB |
1598103 | Sep 1981 | GB |
1598130 | Sep 1981 | GB |
2170422 | Aug 1986 | GB |
2275622 | Sep 1994 | GB |
2350070 | Nov 2000 | GB |
9532044 | Nov 1995 | WO |
Number | Date | Country | |
---|---|---|---|
60328984 | Oct 2001 | US |